The use of high frequency filters with associated resonant cavities is well-known in the art.
The invention described herein relates to a duplexing filter for combining filters operating at two different frequencies, such as at 400 MHz and 800 MHz. The concept of placing two high frequency filters in the same resonant housing is unique due to its use of a single feedline from the filter housing to an associated antenna or the like. The potential savings of labor and installation costs associated with a single feedline for both 400 MHz and 800 MHz frequency bands, as opposed to separate feedlines for each of these frequency bands, could be very large.
The present invention achieves this duplexing filter by positioning the high frequency filter approximately half way with respect to the shorted end of the lower frequency coupling line.